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RE: New LFRD/ASD Steel Code (Was: Any Young Engineers Out There?)

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Bill,
Well said.  We have had LSD (Limit States Design) for about 10 years 
more than you had LRFD and it has been mandatory for approx 15 years
but you still need to check stresses occasionally just as the recent 
thread about Von Mises indicated.  There is no question that LSD 
takes longer as you have to track all your dead and live loads 
separately--imagine a Christmas tree with a hundred different 
branches, each with two or three different live loads.  This was 
prompted by the desire to make steel more competitive (lower factor 
of safety on the dead loads and to take into better account counter-
acting loads--the case quoted to me was a transmission tower that 
failed due to over-estimation of dead load.  They said it would not 
have happened with LRFD (it reported to be in the US). I design crane 
runways and dead load is not a significant influence so very little 
is gained by LSD or LRFD and if there was a savings, I am not sure if
it would be a benefit due to fatigue considerations.  Having said 
that, I find that speadsheets make it easier to design in LSD or 
LRFD, and track all the loads.
    For the young engineers, I remember a senior engineer at my first
company saying that the older he got and the more he learned, the 
harder it became to design a simple beam.
Gary

On 24 Jan 2006 at 18:39, Sherman, William wrote:

> I agree with Scott's comments below.  You can calculate actual service
> load stresses the same as always, but the allowable stresses will need
> to be determined under the new code once it is adopted via the building
> codes.  And as an "old engineer" that hoped to retire before having to
> learn LFRD for steel design, it looks like it will be just as easy to
> design per LFRD as per ASD under the new code (or perhaps, just as hard
> to learn to design per ASD under the new code as it is to learn to
> design per LFRD). 
> 
> It is my opinion that codes for all construction materials should
> maintain some basic allowables for design or analysis per ASD.  We
> should never lose the ability to determine "actual stresses" in a
> structural member under applied loads, and we should not lose sight of
> what are appropriate allowable stress ranges when doing such analyses. 
> 
> 
> William C. Sherman, PE
> (Bill Sherman)
> CDM, Denver, CO
> Phone: 303-298-1311
> Fax: 303-293-8236
> email: shermanwc(--nospam--at)cdm.com
> 
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] 
> Sent: Tuesday, January 24, 2006 12:53 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Any Young Engineers Out There?
> 
> Ya, but they will be taking it off that shelf in the not so distant
> future.  This difference this time is that future model building codes
> (i.e. starting with 2006 IBC, I believe) will not longer reference the
> 1989 AISC ASD spec as "permitted"/"legal" design.  All current codes
> that I aware of that are in effect (i.e. legally adopted by local
> jurisdications) still reference the 1989 AISC ASD spec (sometimes they
> also reference the Supplement 1 to the ASD spec that was officially
> released in December 2001 although it did not really modify all that
> much) along with a version of the LRFD spec.  Thus, you can right now
> "legally"
> design using the 1989 ASD spec.  This is largely due to AISC not
> updating the ASD spec and not being able (or wanting to...maybe) "kill"
> it from the model building codes.
> 
> That is until now...
> 
> Now they have an updated spec that updates both ASD and LRFD and that is
> what will be referenced in future model (i.e. IBC) building codes.  And
> when that happens, we will all be "forced" (although I have no doubt
> that some will continue to use "old" ASD) to use the new spec.  Now, it
> will not happen right away cause even once a model building code adopts
> the new spec (which I believe that the 2006 IBC has done), it takes time
> for many local jurisdictions/states to adopt that model building code.
> 
> So, enjoy your reprieve and relish your last, limited time with 1989 ASD
> (and thus "Green Book") spec.  You will likely be delving into the 2005
> ASD/LRFD spec relatively soon, be that either in the form of a free PDF
> from AISC or in your brand spaking new 13th edition AISC manual
> (assuming that they ever ship them...sorry Charlie...could not help
> myself <grin>).
> 
> Now, the interesting question I think is: how many people will make the
> switch to LRFD when they are force to learn the new 2005 ASD/LRFD spec?
> After all, the only really difference between "using" ASD and LRFD will
> be whether or not you want to put load factors on your load calculations
> on the "demand side".  The "capacity" side of the equation will be
> virtually identical.
> 
> Regards,
> 
> Scott
> Adrian, MI
> 
> 
> On Tue, 24 Jan 2006, Polhemus, Bill wrote:
> 
> > Here's the question that I want to see answered...and mark my words, 
> > it will probably be asked before a year has gone by:
> >
> > "How many engineers here--regardless of age--took one look at the new 
> > Thirteenth Edition AISC Manual of Steel Construction, put it up on 
> > their bookshelves and went right back to the Ninth Edition?"
> >
> > (N.B. It's gonna take forty years traveling in the wilderness, like 
> > Moses and the children of Israel, before the last vestiges of the ASD 
> > Idolatry are snuffed out).
> 
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